Electrophotographic imaging members, i.e., photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the dark so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated. A latent image is formed on the photoreceptor by first uniformly depositing electric charges over the surface of the photoconductive layer by one of any suitable means known in the art. The photoconductive layer functions as a charge storage capacitor with charge on its free surface and an equal charge of opposite polarity (the counter charge) on the conductive substrate. A light image is then projected onto the photoconductive layer. On those portions of the photoconductive layer that are exposed to light, the electric charge is conducted through the layer reducing the surface charge. The portions of the surface of the photoconductor not exposed to light retain their surface charge. The quantity of electric charge at any particular area of the photoconductive surface is inversely related to the illumination incident thereon, thus forming an electrostatic latent image.
The photo-induced discharge of the photoconductive layer requires that the layer photogenerate conductive charge and transport this charge through the layer thereby neutralizing the charge on the surface. Two types of photoreceptor structures have been employed: multilayer structures wherein separate layers perform the functions of charge generation and charge transport, respectively, reference, for example, U.S. Pat. Nos. 6,824,940; 6,787,277; and 6,677,909, the disclosures of each of which are totally incorporated by reference herein; and single layer structures in which photoconductors perform both charge generation and charge transport functions. These layers are formed on an electrically conductive substrate and may include an optional charge blocking layer and an adhesive layer between the conductive substrate and the photoconductive layer or layers. Additionally, the substrate may comprise a non-conducting mechanical support with a conductive surface. Other layers for providing special functions such as incoherent reflection of laser light, dot patterns for pictorial imaging, or subbing layers to provide chemical sealing and/or a smooth coating surface may also be employed.
One problem encountered with multilayered photoreceptors comprising a charge generating layer and the charge transport layer is that the thickness of the charge transport layer, which is normally the outermost layer, tends to become thinner during image cycling. This change in thickness causes changes in the electrical properties of the photoreceptor. Thus, in order to maintain image quality, complex and sophisticated electronic equipment is necessary in the imaging machine to compensate for the electrical changes. This increases the complexity of the machine, cost of the machine, size of the footprint occupied by the machine, and the like. Without proper compensation of the changing electrical properties of the photoreceptor during cycling, the quality of the images formed degrades due to spreading of the charge pattern on the surface of the imaging member and a decline in image resolution. High quality images are essential for digital copiers, duplicators, printers, and facsimile machines, particularly laser exposure machines that demand high resolutions images.
To achieve long life in conventional multilayer photoreceptors, several advanced concepts such as protective overcoat and wear resistant fillers in the charge transport layer have been pursued.
Alternatively, owing to their top-photogeneration mechanism, a long operating life is also feasible using single layer organic photoreceptors, with thicknesses of, for example, about 25 micrometers to about 40 micrometers. Another method of extending photoreceptor life is by using a thick one layer device, typically based on organic materials.
The majority of single layer organic photoreceptors generally comprise thermoplastic binders. Typically, a single layer organic photoreceptor comprises a photogenerating pigment, a thermoplastic binder, and hole and electron transport materials. Single layer organic photoreceptors have many advantages over multilayer photoreceptors in manufacturing costs, total cost of ownership, environmental friendliness, and print quality. The photogeneration mechanism is at the top or near the top of the photoreceptor surface, and therefore the photoreceptor is less prone to problems or variants associated with substrate related and thickness dependent photoelectrical properties. Top photogeneration also allows thick devices to be implemented as dictated by constraints of photoinduced discharge properties.
U.S. Pat. No. 6,656,650 of Liang-Bih Lin, Helen R. Cherniack, John S. Chambers, Anna M. Main, Huoy-Jen Yuh, Cindy C. Chen, James M. Duff, Timothy P. Bender describes in the Abstract thereof a member including, for example, a supporting layer and a single photogenerating layer, the photogenerating layer comprising particles including hydroxygallium phthalocyanine phthalocyanine Type V, x polymorph metal free phthalocyanine, or chlorogallium phthalocyanine dispersed in a matrix comprising an arylamine hole transporter and an electron transporter selected from the group consisting of N,N′bis(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide, 1,1′-dioxo-2-(4-methylphenyl)-6-phenyl-4-(dicyanomethylidene)thiopyran, and a quinone selected from the group consisting of carboxybenzylhaphthaquinone, and tetra (t-butyl) diphenoquinone, and mixtures thereof, and submicrometer size polytetrafluroethylene particles, and a film forming binder.
U.S. Pat. No. 5,370,953 describes in the Abstract thereof an electrophotosensitive material comprising a conductive substrate, a photosensitive layer formed on the conductive substrate and, if necessary, a surface protective layer formed on the photosensitive layer, wherein an oxadiazole derivative expressed in a general formula (I):

where R1 denotes an alkyl group, is contained as an electron transfer substance on the photosensitive layer and/or surface protective layer. This photosensitive material enhances the electron transfer capability, and hence the sensitivity is improved. At the same time, the residual potential of the photosensitive material is lowered, and the stability and durability against repeated exposures are enhanced.
U.S. Pat. No. 5,336,577 describes in the Abstract a thick organic ambipolar layer on a photoresponsive device is simultaneously capable of charge generation and charge transport. In particular, the organic photoresponsive layer contains an electron transport material such as a fluorenylidene malonitrile derivative and a hole transport material such as a dihydroxy tetraphenyl benzadine containing polymer. These may be complexed to provide photoresponsivity, and/or a photoresponsive pigment or dye may also be included.
U.S. Pat. No. 5,700,614 describes in the Abstract cyclopentadiene derivative compounds, and an electrophotographic photoconductor comprising one cyclopentadiene derivative compound are disclosed. The cyclopentadiene derivative compounds are useful for use in a photoconductive layer, and readily soluble in a binder resin. The electrophotographic photoconductor can be prepared by using a simple, effective production method. The electrophotographic photoconductor comprising one cyclopentadiene derivative compound provides a good light sensitivity and high durability.
U.S. Pat. No. 5,968,696 describes in the Abstract a single-layer binder comprising a synthetic resin binder and a phthalocyanine pigment dispersed therein modified so as to reduce the content of the phthalocyanine pigment while maintaining or further improving the sensitivity of the binder. A coating material comprising a synthetic resin binder comprising as a constituent component a polyester resin containing halogen atoms, e.g., chlorine or bromine, and a phthalocyanine pigment dispersed in the binder is applied to a conductive base to produce an electrophotographic binder.
The disclosures of each of the foregoing U.S. Patents are each incorporated herein by reference in their entireties. The appropriate components and process aspects of the each of the foregoing U.S. Patents may be selected for the present invention in embodiments thereof.
There remains a need for a single layer electrophotographic imaging member having a long and robust service life. As employed herein, the expression “single layer photogenerating imaging member (or layer)” is defined as a single electrophotographically active layer capable of retaining an electrostatic charge in the dark during electrostatic charging, imagewise exposure, and image development. Further, there remains a need for an electrophotographic imaging member having a tough, abrasion resistant durable surface for high quality imaging while simultaneously achieving very low total cost of ownership and unit manufacturing cost.